Sedimentation Process- Part 01

Summary

This session covers the water treatment process, focusing on sedimentation. It introduces key concepts such as the theory of sedimentation, settling types, and sedimentation tanks. The process of removing suspended particles through gravity is explained, highlighting plain sedimentation and sedimentation with coagulation. Various types of settling—discrete, flocculating, hindered zone, and compression settling—are discussed. The session also explores different sedimentation tanks, including rectangular, circular, and hopper-bottom tanks, emphasizing their design and functions. The importance of inlet and outlet arrangements, as well as sedimentation zones, is also covered to provide a comprehensive understanding of sedimentation in water treatment.

Takeaways

• 😀 Sedimentation is a process used in water treatment to remove suspended impurities by allowing particles to settle due to gravity.
• 😀 The detention period is the time water is kept still in the sedimentation tank to allow particles to settle.
• 😀 There are two main types of sedimentation: plain sedimentation and sedimentation with coagulation.
• 😀 Plain sedimentation relies on gravity alone to remove impurities, while sedimentation with coagulation involves chemicals to form and remove particles (flocs).
• 😀 The settling of particles depends on characteristics like particle size, shape, specific gravity, and concentration, with four types of settling: discrete particles, flocculating particles, hindered zone settling, and compression settling.
• 😀 Discrete particles settle individually, flocculating particles form larger clusters that settle faster, and hindered zone settling occurs when particles settle as a group.
• 😀 Compression settling happens when particles are highly concentrated and settle through compaction, requiring external pressure.
• 😀 Sedimentation tanks can be intermittent (quiescent tanks) or continuous, with continuous flow tanks preferred for efficiency.
• 😀 Types of sedimentation tanks include rectangular, circular, and hopper-bottom (vertical) tanks, each with different flow patterns and advantages.
• 😀 Rectangular tanks are commonly used and are designed to reduce flow velocity, with sludge removal facilitated by mechanical scrapers.
• 😀 Circular sedimentation tanks allow water to flow radially, helping particles settle more effectively, with simpler sludge removal mechanisms.
• 😀 Hopper-bottom tanks involve vertical flow, where particles settle due to gravity and are removed from the tank's bottom through a sludge outlet.
• 😀 Sedimentation tanks are divided into four zones: the inlet zone, settling zone, outlet zone, and sludge zone, each serving a specific function in the sedimentation process.
• 😀 Inlet arrangements with baffle walls are used to ensure smooth flow and reduce velocity, while outlet devices maintain uniform velocity to prevent short-circuiting.
• 😀 The session provided a comprehensive overview of sedimentation, including its theory, types, tank designs, and functional zones in sedimentation tanks.

Q & A

What is sedimentation in water treatment?

Sedimentation is the process of removing suspended particles from water by allowing them to settle down under the influence of gravity, typically in a settling tank. This process helps separate suspended solids from liquid, improving water quality.

What are the main objectives of sedimentation?

The main objective of sedimentation is to separate suspended solids from water by using gravity. The suspended particles settle at the bottom of the tank, leading to clearer water.

What are the two types of sedimentation processes?

The two types of sedimentation are plain sedimentation, where impurities are removed by gravity alone, and sedimentation with coagulation, where chemicals are added to the water to form flocs, which then settle out.

What factors determine the type of settling process used?

The type of settling process depends on the characteristics and concentration of the particles in suspension. The four types of settling are discrete particles, flocculating particles, hindered zone settling, and compression settling.

What is the difference between discrete particle settling and flocculating particle settling?

In discrete particle settling, individual particles settle independently without interacting with others, while in flocculating particle settling, particles clump together to form larger masses or flocs that settle faster.

What are the types of settling tanks used in water treatment?

There are three main types of sedimentation tanks: rectangular tanks, circular tanks, and hopper bottom (vertical) tanks. Each type has different flow characteristics and is chosen based on the specific needs of the water treatment process.

Why are rectangular tanks typically preferred for sedimentation?

Rectangular tanks are preferred because they are hydraulically stable, easy to control for larger volumes of water, and the flow is more uniform, making the sedimentation process more effective.

How does the flow differ in circular tanks compared to rectangular tanks?

In circular tanks, water enters from the center and flows radially towards the perimeter, where the velocity decreases, allowing particles to settle effectively. In contrast, rectangular tanks have horizontal flow paths, with water moving from one end to the other.

What is the role of baffle walls in sedimentation tanks?

Baffle walls are used to reduce the velocity of incoming water and ensure smooth, uniform flow through the tank. This helps in minimizing turbulence and optimizing the settling process.

What are the four zones in a sedimentation tank, and what are their functions?

The four zones in a sedimentation tank are: the inlet zone (where water enters and is distributed), the settling zone (where particles settle), the outlet zone (where clarified water exits), and the sludge zone (where accumulated sludge is collected). These zones help in the efficient functioning of the tank.